1. Field of the Invention
The present invention relates to a flame retarded epoxy resin composition, which is characterized by that said flame retarded epoxy resin composition comprising A) at least one type of epoxy resin and (B) a phosphorus-and-nitrogen-containing heterocyclic compound having a moiety which can react with the epoxy group of the epoxy resin and useful as a hardening agent for epoxy resin.
The flame retarded epoxy resin composition mentioned above can reach the standard for flame retarded property of UL94V-0 without containing conventional flame retarded materials such as halides, antimony trioxide and the like. Thus, the said resin composition with excellent flame retarded properties is suitably used as the heat-resistant or flame-retarded materials required in the manufacture of electronic products, electric products, and automobile parts, and for other related applications.
2. Background of the Invention
While to the well known conventional epoxide has a limited usage range due to its combustible character, it has been known that the flame retarded property can be improved by adding resins containing halogen or haloalkyl group to the epoxide. In order to improve the flame retarded property of polymers or compositions thereof, flame retarded materials such as halo-organic compounds or oxides containing antimony or vanadium have traditionally been widely used to form high heat resistant compositions, however, the addition of such halo resins or polymers or metal (such as antimony) oxide is required in large amounts to attain the requirements for the flame retarded property.
Due to easy processability, high safety, and excellent mechanical and chemical properties, epoxy resins have been widely used in many fields, for example, in the application of composite material, such as coating, electrical insulation, construction, building materials, adhesives or laminated products. Further, now epoxy resins also can be used to make laminated plates for having strong adhesion to reinforcement materials (such as glass-fiber fabric) and no volatile elements formed and small shrinkage in hardening. On the other hand, laminated plates produced by epoxy resins have been massively applied to the component materials for electrical and electronic products and their other components.
In addition to a requirement to produce accurate and fine patterns on circuit boards, laminated plates are required to have excellent electrical properties, mechanical properties, and heat resistant processabilities for the currently significant manufacturing process of the printed circuit board. Most of widely used FR4 laminated plates or resin-coated copper foil for build-up process have a glass transition temperature of about 130xc2x0 C. after hardening. In the manufacturing process of the printed circuit board, the temperature is over 200xc2x0 C. during cutting and drilling, and even over 270xc2x0 C. during welding, which may make laminated plates break or crack during the manufacturing process. Therefore, various resins which possess high heat stability and high glass transition temperature have been developed. In addition, for the laminated plates of printed circuit board, another important property is flame retardancy, which is absolutely necessary in some applications such as in airplanes, automobiles, and other items of public transportation.
In order to impart the flame retarded property to the material for laminated plates, substances that put out flames and decrease burning should be introduced. For the laminated plates of epoxy resin/glass-fiber systems (or organic fiber) or dielectric materials for build-up process, generally halogen-containing compounds, particularly bromine-containing epoxy resins and hardeners, are added in combination with flame retardants, such as diantimony trioxide and the like, to achieve the strict flame retarded standards (as the UL94V-0 level) in the laminated plates. The flame retarded substance in epoxy resin usually required to contain up to 21% of bromine, is used in combination with diantimony trioxide or other retardants to attain the standard of UL 94V-0. However, it is harmful to human health for using high contents of bromine in epoxy resin or diantimony trioxide. Additionally, toxic smokes of erosive free radicals and hydrogen bromide generated by bromine burning, and also toxic furan bromides and a dioxine bromide compound produced from aromatic compounds with high bromine contents during burning seriously affect human health and the environment. Accordingly, it is most urgent to find a novel flame retarded material and a method to provide flame retarded properties to solve the pollution and environmental problems caused by the current use of laminated products or components containing bromide or bromo-epoxy resin. Especially, corresponding to the massive use of FR-4 epoxy glass fiber laminated plates for electronic and electric products and components, it is necessary to actively develop flame retarded epoxy resin materials which will not endanger human beings and are environmentally protective.
Recently, in order to protect human health and decrease the sources of environmental pollution, various new flame retarded materials have been developed, wherein the technique is widely accepted for using phosphorus-containing compounds instead of those conventionally used flame retarded materials such as bromine-containing compounds. Currently phosphorus system compounds have been extensively studied and applied as the new generation of flame retarded materials with environmental-protective concepts. For example, red phosphorus or phosphorus-containing organic compounds (such as triphenyl phosphate, triphenylmethyl phosphate, etc.) are directly added to substitute halide compounds as a flame retarder to improve the burning property of polymer materials or hardening resin materials. However, addition of such flame retarded compounds in large amounts direct into resins is always required to achieve the effect of flame retardancy. Due to the smaller molecular weight of the compound, higher migration will affect the properties of resin substrates, for example, to worse electrical properties, adhesive strength, heat resistance, etc., and result in difficulty in application.
Later techniques using a reactive type of phosphorus-containing epoxy resin instead of bromine-containing or bromo-epoxy resins generally used as flame retarded ingredients have been developed. For example, in U.S. Pat. No. 5,376,453, laminated plates, which are produced by using a composition of phosphates with epoxy groups and nitrogen-containing hardening agents, need to be added with various phosphate-containing epoxy resins to increase phosphorus content to achieve the strict burning standard of UL 94V-0. In U.S. Pat. No. 5,458,978, a composition formed from epoxy phosphates, nitrogen-containing epoxy resin, and metal complex hardener is used to make laminated plates which have a glass transition temperature of about 175xc2x0 C. and a flame retarded property similar to that of UL 94V-0 (42 seconds, 50 seconds related to critical value). In U.S. Pat. Nos. 4,973,631 and 5,086,156, a trialkyl oxide having an active hydrogen substituent (such as an amino group) is used alone or in combination with other amine hardeners to harden epoxy resins; by means of such a hardening method to introduce phosphorus to resins, however, a proper flame retarded effect can not be achieved due to the lower content of phosphorus; and there is no actual measurement of the flame retardant effect in these two patents. According to the techniques disclosed in the above patents, it is realized that addition of various or high contents of phosphorus-containing compounds is usually required to meet the flame retarded standard, however, various additional additives usually make the processing conditions of products difficult to control or the quality of products inferior.
Therefore, the method to increase flame retarded property employs a nitrogen- and phosphorus-containing substance instead of traditional bromine- or antimony-containing substances.
In accordance with environmental problems generated by flame retarded materials previously added with toxic substances containing halogens or antimony, the inventor of the present invention has developed a flame retarded compound corresponding to the environmentally protective requirements. The said compound is a phosphorus- and nitrogen-containing heterocyclic compound, and structurally has a moiety reactive with the epoxy group of an epoxy resin, and can be used as a hardener component of the epoxy resin composition.
According to the present invention, it has been found to increase the heat resistance of the epoxy resin composition by adding effective amounts of phosphorus- and nitrogen-containing heterocyclic compounds to epoxy resin. Besides having improved flame retarded properties, the epoxy resin composition formed by the foregoing phosphorus- and nitrogen-containing compound and the epoxy resin can also have the effect of increasing electric and mechanical properties, and have excellent processing properties. Accordingly, the production cost can be reduced because no large amount of flame retarded additives is required. In addition, such flame retarded resin compositions having a high glass transition temperature and excellent heat resistance are suitably used for production of prepregs with flame retarded properties, laminated layers, dielectric materials for build-up process and materials for printed circuit boards.
The present invention relates to a flame retarded epoxy resin composition, which is characterized by comprising:
(A) at least one type of epoxy resin;
(B) a phosphorus-and-nitrogen-containing heterocyclic compound, said compound having a moiety which can react with the epoxy group of epoxy resin and can be used as a hardening agent for epoxy resin. The structure is as shown by formula (I): 
wherein m is an integer of from 0 to 2, n is an integer of from 3 to 7, but at least one m is not 2.
The flame retarded epoxy resin composition composed of the above components (A) and (B) has improved flame retardency and is suitable for flame retarded materials required for such as composite materials, laminated layers, printed circuit boards, electronic and electric product components. Additional additives such as hardening agents, which do not contain phosphorus, hardening promoters, solvents, etc can be added selectively according to the fields of application.
In the present invention, (A) epoxy resin component of the composition can be a general epoxide, including an epoxy resin composed of one or more epoxides, wherein said epoxy resin is characterized by an epoxy equivalent weight of less than 600. The types of epoxy resin useful in the present invention comprise the epoxides containing an epoxy group modified by the moiety such as bisphenol, phenol, dihydroxy-benzene, bis(biphenol), naphthalene, alkyl, alkenyl, nitrogen-containing heterocyclics, cresol-aldehyde, phenolic aldehyde resin, siloxane or polysiloxane, and aryl phosphate.
In the flame retarded epoxy resin composition of the present invention, the types of epoxy resin component having epoxy groups comprise glycidyl ether, glycidyl amine, glycidyl thio-ether, glycidyl carbonate, and the like, wherein the glycidyl ether modified by bisphenol, bis(biphenol), dihydroxybenzene, polyol, or silicone is preferred.
In the present invention the examples of such glycidyl ether modified by the specific groups, in the embodiment, comprise bisphenol-modified diglycidyl ether having xe2x80x94Phxe2x80x94Xxe2x80x94Phxe2x80x94 (wherein X is CH2, C(CH3)2, CH(CH3), O, S, CO, or SO2) moiety, such as bisphenol A glycidyl ether, bisphenol F glycidyl ether, bisphenol AD glycidyl ether, bisphenol S glycidyl ether, tetramethyl bisphenol A glycidyl ether, tetramethyl bisphenol F glycidyl ether, tetramethyl bisphenol AD glycidyl ether, tetramethyl bisphenol S glycidyl ether, and the like. The examples of bis(bisphenol)-modified diglycidyl ether, in the embodiment of the present invention, comprise 4,4xe2x80x2-biphenyl glycidyl ether, 3,3xe2x80x2-dimethyl-4,4xe2x80x2-biphenyl glycidyl ether, 3,3xe2x80x2,5,5xe2x80x2-tetramethyl-4,4xe2x80x2-biphenyl glycidyl ether, etc. The examples of dihydroxy-benzene glycidyl ether, in the embodiment of the present invention, comprise resorcinol glycidyl ether, quinol glycidyl ether, and isobutyldihydroxybenzene glycidyl ether. The examples of phenolic aldehyde polyglycidyl ether, in the embodiment of the present invention, comprise phenol aldehyde polyglycidyl ether, cresol phenolic polyglycidyl ether, and bisphenol A phenolic polyglycidyl ether. The embodimental examples of polyhydroxyl-modified polyglycidyl ether comprise tris(4-hydroxyphenyl)methane polyglycidyl ether, tris(4-hydroxyphenyl)ethane polyglycidyl ether, tris(4-hydroxyphenyl)propane polyglycidyl ether, tris(4-hydroxyphenyl)butane polyglycidyl ether, tris(3-methyl-4-hydroxyphenyl)methane polyglycidyl ether, tris(3,5-dimethyl-4-hydroxyphenyl)methane polyglycidyl ether, tetrakis(4-hydroxyphenyl)ethane polyglycidyl ether, tetrakis(3,5-dimethyl-4-hydroxyphenyl)ethane polyglycidyl ether, etc. The epoxy resin mentioned above can be used alone or in combination as the mixture of two or more epoxy resins.
In the present invention, the foregoing epoxy resin component, preferably bifunctional bisphenol A polyglycidyl ether, resorcinol glycidyl ether, trifunctional tri(4-hydroxylphenyl)methane polyglycidyl ether, tetrafunctional tetra(4-hydroxylphenyl)ethane polyglycidyl ether, or cresol phenolic polyglycidyl ether, can be used alone or in combination as the mixture of two or more epoxy resins.
Further, the epoxy resin component in the present invention can be modified with silicones or rubber copolymers. The foregoing silicones compounds are such as siloxane with amino ending group (for example, trade name SF-8012, commercially available from Shin-Etsu Company, Japan). The rubber copolymers mentioned above are such as the carboxyl ending group copolymer of butadiene and acrylonitrile (for example, trade name CTBN, commercially available from Goodrich Company, USA) or the amino ending group copolymer of butadiene and acrylonitrile (for example, trade name CTBN, commercially available from Goodrich Company, USA).
In the flame retarded epoxy resin composition of the present invention, (B) phosphorus-and-nitrogen-containing heterocyclic compound is used to increase flame retardency and heat resistance. Said compound has a moiety which can react with the epoxy group of the epoxy resin, and can be used as an epoxy resin hardening agent. The structure is as shown in formula (I): 
wherein m is an integer of from 0 to 2, n is an integer of from 3 to 7, but at least one m is not 2.
The ratio of (A) epoxy resin and (B) phosphorus-and-nitrogen-containing heterocyclic compound in the flame retarded epoxy resin composition of the present invention is such that, for the added amount of (B) phosphorus-and-nitrogen-containing heterocyclic compound having a moiety which can react with the epoxy group, according to the reactive hydrogen equivalent weight and epoxy equivalent weight of epoxy resin (A), the reactive hydrogen equivalent weight of the hardening agent (B) is from 20% to 95%, preferably from 40% to 90%, more preferably from 50% to 90%, related to the epoxy equivalent weight of 100%.
Additionally, the flame retarded epoxy resin composition of the present invention can be further added with (C) hardening agents, which do not contain phosphorus, (D) hardening promoters, (E) solvents, and (F) other additives which comply into high heat-resistant materials in various fields, such as applied in laminates, IC packaging materials, high heat resistant powder coating, and the like. Further, the viscosity can be controlled by adding solvents to formulate the type of varnish for use in the manufacturing of prepregs, laminates, dielectric materials for build-up process.
Suitable hardening agents, which do not contain phosphorus, comprise substances such as polyol, polyamine, polythiol, polycarbonates, and the like containing bisphenol, dihydroxybenzene, phenol, naphthalene, alkene, cyclohydrocarbon, nitrogen-containing heterocyclics, phenolic aldehyde resin, siloxane, polysiloxane, and having xe2x80x94Phxe2x80x94Xxe2x80x94Phxe2x80x94 (wherein X is CH2, C(CH3)2, CH(CH3), O, S, CO, or SO2) moiety. Also, hardening agents, which do not contain phosphorus, comprise amines, polyhydroxylphenols, and phenolic aldehydes. The examples of amines, in the embodiment, comprise dicyandiamide (NH2C(NH)(NHCN)), diaminodiphenylmethane (DDM), and etc. Polyhydroxyl phenols comprise tris(4-hydroxyphenyl)methane, tris(4-hydroxyphenyl)ethane, tris(4-hydroxyphenyl)propane, tris(4-hydroxyphenyl)butane, tris(3-methyl-4-hydroxyphenyl)methane, tris(3,5-dimethyl-4-hydroxyphenyl)methane, tetrakis(4-hydroxyphenyl)ethane, tetrakis(3,5-dimethyl-4-hydroxyphenyl)ethane, and the like. The examples of phenolic aldehyde, in the embodiment, comprise phenol formaldehyde condensates, cresol phenolic condensates, and bisphenol A phenolic aldehyde condensates, etc.
The frequently used hardening agents, which do not contain phosphorus, are such as dicyandiamide (NH2C(NH)(NHCN)), diaminodiphenylmethane (DDM), diethyltriamine (DETA), diaminodibenzenesulfone (DDS), m-phenyldiamine (MPDA), methyl diphenylamine (MDA), maleic acid (MA), phthalic acid (PA), hexahydrophthalic acid (HHPA), tetrahydrophthalic acid (THPA), and the like.
The content of foregoing hardening agents, which do not contain phosphorus, is such that, according to reactive hydrogen equivalent weight of hardening agents, which do not contain phosphorus, and epoxy equivalent weight of epoxy resin, the reactive hydrogen equivalent weight of hardening agents, which do not contain phosphorus, is from 20% to 95%, preferably from 40% to 90%, and more preferably from 50% to 90%, related to the epoxy equivalent weight of epoxy resin of 100%.
In the flame retarded epoxy resin composition of the present invention, a hardening promoter can also be optionally added. Suitable hardening promoters comprise tertiary amines, tertiary phosphines, quaternary ammonium salts, quaternary phosphonium salts, and imidazole compounds, or mixtures thereof. The examples of the tertiary amines, in the embodiment, comprise triethylamine, tributylamine, dimethylaminoethanol, tris(N,N-dimethylaminomethyl)phenol, N,N-dimethylaminomethylphenol, etc. The examples of the tertiary phosphines, in the embodiment, comprise triphenylphosphine, etc. The examples of the quaternary ammonium salts, in the embodiment, comprise tetramethylammonium chloride, tetramethylammonium bromide, tetramethylammonium iodide, triethylbenzylammonium chloride, triethylbenzylammonium bromide, triethylbenzylammonium iodide, etc. The examples of the quaternary phosphonium salts, in the embodiment, comprise tetrabutylphosphonium chloride, tetrabutylphosphonium bromide, tetrabutylphosphonium iodide, tetrabutylphosphonium acetate complex, tetraphenylphosphonium chloride, tetraphenylphosphonium bromide, tetraphenylphosphonium iodide, ethyltriphenylphosphonium chloride, ethyltriphenylphosphonium bromide, ethyltriphenylphosphonium iodide, ethyltriphenylphosphonium acetate complex, ethyltriphenylphosphonium phosphate complex, propyltriphenylphosphonium chloride, propyltriphenylphosphonium bromide, propyltriphenylphosphonium iodide, butyltriphenylphosphonium chloride, butyltriphenylphosphonium bromide, butyltriphenylphosphonium iodide, etc. The imidazole compounds comprise 2-methylimidazole, 2-phenylimidazole, 2-ethyl-4-methylimidazole, 2-dodecyl-imidazole, 2-heptadecyl-imidazole, etc. Hardening promoters are preferably tertiary phosphines, and imidazole compounds, more preferably 2-methylimidazole, 2-phenylimidazole, ethyltriphenylphosphonium acetate complex, and butyltriphenylphosphonium bromide. The hardening promoter mentioned above can be use alone or in the form of a mixture thereof.
The optionally added amount of hardening promoters in the flame retarded epoxy resin composition of the present invention is from 0.005% to 5.0% by weight, preferably from 0.05% to 4.5% by weight, more preferably from 0.1% to 4.0% by weight, most preferably from 0.15% to 3.0% by weight of the total weight of the composition.
If the added amount of hardening promoters to the composition of the present invention is more than 5.0% by weight, it will shorten the reaction time but cause bad influence on the production of by-products and the consistency for the transforming rate of hardening reaction. If the hardening promoter content of the composition is less than 0.005% by weight, the reaction will be too slow to be efficient.
The flame retarded epoxy resin composition of the present invention can be added with solvents to form varnish. Adding solvents can adjust the viscosity of the epoxy resin composition of the present invention to from 20 to 500 cps/25xc2x0 C. as an advantage for the production of prepregs by means of impregnation and drying or for the coating of dielectric layer for build-up process.
Suitable solvents for the formulation of varnish are organobenzenes, ketones, non-protonic solvents, ethers, esters, etc. Organobenzenes comprise toluene and xylene. Ketones comprise acetone, methyl ethyl ketone, and methyl isobutyl ketone. Nonprotonic solvents comprise N,N-dimethyl formamide and N,N-diethyl formamide. Ethers comprise ethanediol monomethyl ether and propanediol monomethyl ether. Esters comprise ethyl acetate and ethyl isopropionate.
Generally, the addition of the hardening promoters and the selectively added solvents to formulate the varnish of the composition of the present invention allows the viscosity to be controlled in the range of from 20 to 500 cps/25xc2x0 C. and the gelation time to be controlled in the range of from 30 to 500 sec/171xc2x0 C.
According to the applications and some specific uses, the flame retarded epoxy resin composition of the present invention can be added with general commercial additives or modifiers, for example, heat stabilizers, light stabilizers, UV absorbents, plasticizers, or inorganic fillers, etc. Although additives or modifiers containing halogen or antimony trioxide are also available, it is no suggested to use such additives in the composition of the present invention in view of the problems of environmental protection and toxicity.
After formulating the flame retarded epoxy resin composition disclosed in the present invention into varnish, laminates can be formed by can be laminated with copper foils, fiber supporters and the flame retarded epoxy resin composition containing phosphorus and nitrogen compound by the methods known in the art. A fibrous substrate can be impregnated with the flame retarded epoxy resin composition of the present invention. The fibrous substrate can be organic or inorganic material such as glass, metal, carbon fiber, inorganic fiber (for example, boron fiber), cellophane, cellulose, and organic polymer material, etc. For example, after the glass fiber fabric is impregnated with the epoxy resin composition varnish of the present invention, it is then dried by heating, giving a dry prepreg; such prepregs having excellent storage stabilities can be stored for months under room temperature. The prepreg can further be shaped into composite material laminated plates or used alone in the adhesive layer of other prepregs, or used in the combination of one or more prepregs with copper foil placed on one or both sides. The resulting laminated plate composite material, obtained by heating the prepreg or the combination under pressure, has significant improvement and superiority to the standards of current products in respect to size stability, resistance to chemicals, resistance to corrosion, moisture absorption, and electrical properties, and is suitable for producing products or parts for electronics, electrics, space, and transport, for example, for manufacturing printed circuit boards and multi-layer circuit boards, etc; or resin-coated() copper foils for build-up process are made on copper foils by means of the precisely coating method; or dielectric films for build-up process are made by means of coating on releasing films. For example, glass fibrous fabric can be impregnated with the phosphorus-containing epoxy resin composition varnish, or the epoxy resin composition varnish may be coated on copper foil, then dried by heating, giving a dry resin-coated() copper foil for build-up process. Such resin-coated copper foils for build-up process with good storage stabilities can be stored at room temperature for months, and can be used to manufacture light, thin and small high density products of printed circuits boards by means of a hot pressure process.
The method for producing the flame retarded epoxy resin composition of the present invention allows said composition to harden at a reaction temperature of from 20 to 350xc2x0 C., preferably of from 50 to 300xc2x0 C., more preferably of from 100 to 250xc2x0 C., and most preferably of from 120 to 220xc2x0 C.
The above-mentioned reaction temperature for hardening must be controlled carefully. If the temperature is above 350xc2x0 C., there will easily be a side reaction where it will be difficult to control the reaction speed, and where the deterioration speed of the resin may be increased; if the temperature is less than 20xc2x0 C., in addition to the poor efficiency, it will be more difficult for the resulting resin to meet the required property for usage under high temperature.
The phosphorus-containing flame retarded epoxy resin composition of the present invention can simultaneously improve the flame retarded property and the heat resistance of the epoxy resin without adding other processing auxiliary agents and flame retarded additives. The present invention also provides a phosphorus-and-nitrogen-containing heterocyclic compounds having a functional group reactive with an epoxy group, which allows the epoxy resin composition containing phosphorus and nitrogen heterocyclic compounds and other epoxy resin composition s containing phosphorus and nitrogen compounds of the present invention to have higher flame retarded property, higher heat resistance, and better mechanical properties than the prior art.